Electronics > Electronics

My ready easy PWM 12V 3A transistor

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Jon_Thompson:
As it stands, this circuit will positively rip current through the 555 and burn it out. It needs a pre-driver stage before the TIP32A to provide enough juice to fully switch it on.

Don't believe me? Try it!

jwatte:
Yes, try it! You will likely burn some components. Once you see smoke, turn off power, and figure out what parts are smoking, and why. Then replace those parts, make appropriate changes to the circuit, and try again. That is the only way to learn! And, yes, it costs some money in components. That's the (very low) cost of learning. I always buy three of anything; I'll burn the first one; I'll use the second one, and the third one is a spare for unexpected accidents.

Btw: For switching power, you want to use a MOSFET, not a BJT. (BJT is the "normal" kind of transistor you're currently using.) BJTs suck current all the time while they are on. MOSFETs only suck current for a short while while they switch state (to on, or to off.) A 555 might be able to drive the gate of a MOSFET fast enough to make the MOSFET and 555 survive, as long as the duty cycle is OK (say, 200-400 Hz PWM.) A 555 will not be able to drive the base of a power BJT with a hFE of 10 to get to 3A. The hFE means that you need to put 300 mA through the base to get 3A through the collector/emitter.

assassa1221:
OK. Thanks I guess... I give up.
I understand that nobody hasn't invented a working "easy to do it self for cheap pwm" for my specific purpose or that the diy-plan is highly kept as a secret(Meaning that I won't be ever possible to solve this because it is impossible to create it myself.)

That is why I must buy a ready made controller:(and simply copy the product)

* http://dx.com/p/dc-6v-90v-15a-pwm-motor-speed-control-switch-governor-green-black-160094
* http://www.buyincoins.com/new_en/details/new-12v-40v-10a-13khz-pulse-width-modulation-pwm-dc-motor-speed-control-switch-product-11539.html
I should have done it in the first place :-[
Bye

newInRobotics:

--- Quote from: assassa1221 on April 17, 2013, 12:34:08 AM ---I give up.
I understand that nobody hasn't invented a working "easy to do it self for cheap pwm" for my specific purpose or that the diy-plan is highly kept as a secret(Meaning that I won't be ever possible to solve this because it is impossible to create it myself.)
--- End quote ---
What are You on about? This whole thread is explaining You how to achieve it and for some reason You refuse to take that knowledge on-board. Circuit You want to build has been built many times since creation of 555 Timer, which was 41 years ago.

jwatte:
I think what he's looking for is a step-by-step instruction for how to put one together without having to know any electronics.

If you have trouble doing Ohm's law in your head, and don't understand what the hFE of a transistor is, and haven't heard of the difference between a MOSFET and a BJT transistor, then designing the appropriate circuit is likely to be impossible.
Meanwhile, if you know enough electronics to understand those things (which is not particularly hard for a dedicated hobbyist) then the circuit designs itself, and you don't really need to document it, because it's so obvious.

Thus, that's likely a reason why there's no PWM circuit for high current loads available with step-by-step no-understanding-needed instructions.

Although the second hit on google is this image:

It comes from this project description: http://www.apdigitallight.com/2010/08/diy-laser-spirograph-part-2.html
Which I think is a pretty good description of a DIY PWM controller circuit. So saying "there's no DIY project available" really isn't true -- it just shows that you didn't think of putting "pwm controller diy" into Google and following a few of the links.
Other links include this: http://3lectronics.com/wp-content/uploads/2011/11/schematic-pwm-controller-eagle.png  and this: http://3lectronics.com/pwm-controller-regulator-diy-555/

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